1. Field of the Invention
The present invention relates to syringes of the type having a syringe barrel and a piston assembly that travels within the syringe barrel, whereby the advancement of the piston assembly in the syringe barrel displaces material from within the syringe barrel and causes that material to be dispensed.
2. Description of the Prior Art
Syringes are used in a wide variety of applications. As a result, the prior art is replete with a large variety of syringe configurations. Hand held syringes are primarily used for dispensing material in a controlled and confined manner. Common uses of syringes include dispensing medications through a needle, dispensing equal parts of epoxy glue onto a surface and dispensing narrow lines of frosting onto a cake. Typically, most prior art syringes function in the same manner regardless to the material they are used to dispense. A prior art syringe typically has a syringe barrel into which the material to be dispensed is held. A piston assembly is positioned at one end of the syringe barrel. The piston assembly is advanced into the syringe barrel by the application of a manual force. As the piston assembly advances within the syringe barrel, the material within the syringe barrel is displaced. This causes the material to be dispensed from a dispensing port present at the far end of the syringe barrel.
To ensure that material within a syringe barrel does not leak past the advancing piston assembly, the piston assembly typically is designed to seal against the interior of the syringe barrel. A common design for a piston assembly is to make a piston head from an elastomeric material in a shape that is slightly wider at points than is the interior of the syringe barrel. When the piston head is placed within the syringe barrel, the oversized sections of the piston head are compressed and seal against the syringe barrel. The seal created by the piston head is typically both air and fluid impervious.
There are two primary ways to fill a syringe barrel with the material that will be eventually dispensed. For low viscosity material, such as water based medical solutions, the material can be drawn into the syringe barrel by retreating the piston assembly in the syringe barrel and creating a negative pressure in the syringe barrel. However, for higher viscosity materials that do not flow under the force of their own weight, such as epoxy, silicone and similar materials, the creation of a negative pressure in the syringe barrel is insufficient to draw the material into the syringe barrel. Rather, for higher viscosity materials, the piston assembly must be removed. The high viscosity material is then filled into the syringe barrel through the piston port. Once filled with a desired amount of high viscosity material, the piston assembly is reintroduced into the syringe barrel, wherein the piston assembly is used to displace the material through the syringe barrel and out the dispensing port.
As material is filled into a syringe barrel, the material becomes mixed with air. Do to the high viscosity of the material, the air may become entrapped within the material. Furthermore, as the piston assembly is reintroduced into the syringe barrel, the air becomes trapped within the syringe barrel in between the piston assembly and the material to be dispensed. As the high viscosity material is displaced through the dispensing port of the syringe barrel, the material mixes with the trapped air. As a result, the material exiting the syringe barrel may contain numerous air bubbles and gaps caused by larger pockets of air.
One specific application that uses a syringe filled with a high viscosity material is in the field of earpiece modeling. In the process of earpiece modeling, a highly viscous impression material is injected onto the opening of the ear using a syringe. The material is allowed to cure in the ear and is then removed. Once removed, the cured impression material can be used to create a hearing aid ear piece of the appropriate size and shape. A problem that occurs in the prior art is that if air becomes entrapped in the impression material while inside the syringe barrel, then the air may cause bubbles and gaps in the final impression that require that the ear impression either be reformed or repaired prior to its use in making a hearing aid.
A need therefore exists in the art for a syringe device that is capable of dispensing a highly viscous material without having air becoming entrapped within the viscous material. Such a need is satisfied by the present invention as described and claimed below.